1. Field of the Invention
The invention relates to a hydraulic unit having a solenoid valve group.
2. Description of the Prior Art
In the patent application DE 103 16 643 A1, a solenoid valve is described, which includes a solenoid valve cartridge and a magnet assembly. The above-mentioned solenoid valve cartridge includes a cup-shaped housing, a pole core, and an armature, while the magnet assembly includes a coil body and a winding. The magnet assembly is situated around the solenoid valve cartridge and a radial prestressing element is situated between a threaded bushing and a housing of the magnet assembly so that a radial force is exerted on the magnet assembly in such a way that the magnet assembly assumes a predetermined, definite position in relation to the solenoid valve cartridge.
FIG. 1 is an exploded depiction of a hydraulic unit. The solenoid valve group 10 is installed in a fluid block 4 and is composed of a plurality of solenoid valves that are each composed of a solenoid valve cartridge 2 and a magnet assembly 3. The magnet assemblies 3 are mounted on and contacted via a stamped grid 5. This structural assembly, combined with other components to form a mounting control unit 6, is mounted onto the fluid block 4 with the solenoid valve cartridges 2. FIG. 2 shows a solenoid valve for the hydraulic unit according to FIG. 1, which is used for example in an antilock brake system (ABS), a traction control system (TCS), or an electronic stability program system (ESP system). As is clear from FIG. 2, in addition to the magnet assembly 3, which includes a coil body 3.1 with a winding 3.2, an electrical contact 3.3, a housing 3.4, and a covering washer 3.7, the solenoid valve 7 also has a valve cartridge 2, which includes a pole core 2.1, a tappet 2.2, a capsule 2.3, a valve insert 2.4, and a return spring 2.5. During the manufacture of the solenoid valve 7, the capsule 2.3 and the valve insert 2.4 of the valve cartridge 2 are attached to one another by press-fitting and a sealed weld 2.8 hydraulically seals the valve cartridge 2 in relation to the atmosphere. In addition, the valve insert 2.4 absorbs the compressive forces occurring in the hydraulic system and transmits them via a caulking flange 2.9 to a caulking region on the fluid block 4. In addition, the valve insert 2.4 accommodates the so-called valve member 2.6, which includes a sealing seat 2.7 into which the tappet 2.2 plunges in a sealed fashion in order to perform the sealing function of the solenoid valve 7. As is also clear from FIG. 2, an inner circumference of the housing 3.4 with a first diameter 11 constitutes a first contact region 3.5 for an interface between the solenoid valve cartridge 2 and the magnet assembly 3 while an inner circumference of the coil body 3.1 with a second diameter 12 constitutes a second contact region 3.6 for the interface between the solenoid valve cartridge 2 and the magnet assembly 3. Because of the tolerances of the respective parts and the desired simple plug-in assembly, the interface is encumbered with play in the diameters 11 and 12. This means that the relative position between the solenoid valve cartridge 2 and the magnet assembly 3 has a radial degree of freedom that can influence the variation of characteristic function values of the solenoid valve 7: there can be large differences among the solenoid valves 7 of a solenoid valve group 10 when the solenoid valve cartridge 2 and the magnet assembly 3 are centered in relation to each other—which can occur randomly, when the magnet assembly 3 rests against the solenoid valve cartridge 2 on one side, or when the magnet assembly 3 assumes intermediate positions between the two extreme positions.